U.S. Pat. No. 5,386,253 to Fielding, incorporated herein in its entirety by this reference, discusses exemplary projection systems utilizing one or more spatial light modulators (SLMs). As noted in the Fielding patent:                Spatial light modulator devices include so-called “active matrix” devices, comprising an array of light modulating elements, or “light valves,” each of which is controllable by a control signal (usually an electrical signal) to controllably reflect or transmit light in accordance with the control signal. A liquid crystal array is one example of an active matrix device; another example is the deformable mirror device (DMD) developed by Texas Instruments . . . .See Fielding, col. 1, 11. 13-21. Of course, yet other types of light “engines,” or sources, and projectors exist, and various of them may be used in connection with the inventions described herein.        
Regardless of the type of projector used, audiences frequently desire to see images high in detail and richness and low in objectionable artifacts. High resolution and image quality in particular facilitates suspension of disbelief of an audience as to the reality of the projected images. Such quality indeed often is an important factor in the overall success of the motion picture viewing experience among today's audiences.
Providing high resolution images to audiences can be prohibitively expensive in terms of producing the software, and in terms of the hardware necessary to show high resolution images. Imax Corporation, for example, the intended assignee of this application, utilizes not only specialized cameras and projectors, but also seventy millimeter, fifteen perforation film to increase the resolution and quality of projected images.
In some venues, it is desirable to be able to display high resolution moving picture images that are non-film based, such as computer generated graphics, or material captured with electronic cameras. It is particularly prohibitive to display these kinds of high resolution images using conventional electronic projectors (and especially those utilizing SLMs) because it is not technically or economically feasible to produce the necessary spatial light modulators (SLM) at sufficient resolution to match the high resolution of the source material. As well, such electronic projectors frequently fail to furnish the dynamic range and overall brightness of images provided by large-format films.
One approach for displaying high resolution images using electronic projectors is to use a number of smaller display devices arranged so that each individual device projects a portion of the total image. This is the principle behind so-called video walls, which feature a matrix of CRT displays, each one displaying only a subset of a high resolution image. This approach is commonly referred to as display tiling. Another approach is to combine or superimpose two or more sub-images by offsetting individual SLMs by 1/z of a pixel, so that the pixels of one spatial light modulator are positioned to lie between the spaces of the pixels of another SLM. This approach is discussed in U.S. Pat. No. 5,490,009.
While tiling can be accomplished using multiple projection systems, each having a light source, SLM and projection lens, in order to provide the most satisfactory tiling of images, and to accomplish superimposition where very high accuracy of image alignment is needed, it is desirable to combine the multiple SLMs into a single projection apparatus. However, it is also desirable for some components such as the light source and projection lens to be shared. Sharing the light source is desirable because a single light source can typically illuminate a larger solid angle than can be coupled into a single SLM. Sharing of projection lenses is further desirable in order to minimize variations in the image quality produced by multiple SLMs by reducing the number of optical components. In order to do this a means is required to efficiently sub-divide the light from the source and to recombine the output of the multiple SLMs prior to the projection lens. This invention provides systems and methods which enable high efficiency in distributing light from a single source to multiple SLMs and recombining the modulated light for projection onto a screen.